1. Field of the Invention
The invention relates to a planar antenna, and in particular to a mobile telecommunication device with a built-in planar antenna providing multiple frequency bands.
2. Description of the Prior Art
An antenna is indispensable part of a mobile telecommunication device. A planar inverted-F antenna (PIFA) is commonly built into a mobile telecommunication device. As miniature antennas are commonly built into mobile telecommunication devices, planar inverted-F antennas (PIFA) with EGSM (880 MHz–960 MHz), DCS (1710 MHz–1880 MHZ), and PCS (1850 MHZ–1990 MHz) functions are developed accordingly.
A dual-frequency planar inverted-F antenna is disclosed by Liu (IEEE transaction on Antennas and Propagation, Vol. 45, pages 1451–1458, Oct. 10, 1997). A dual-band planar inverted-F patch antenna with a branch-line slit is disclosed by Hsiao (Microwave and Optical Technology Letters, Vol. 32, pages 310–312, Feb. 4, 2002). A dual-frequency PIFA with a rolled radiating arm for GSM-DCS operation is further disclosed by Hsiao (IEEE Antennas and Propagation Society International Symposium, pages 103–106, 2003).
Moreover, a series of studies regarding enhancement of operating bandwidth of PIFA have been made by Virga and Rahmat-Samii (Low-profile enhanced-bandwidth PIFA antennas for wireless communications packaging, IEEE transaction on Microwave Theory and Techniques, Vol. 45, pages 1879–1888, Oct. 10, 1997).
A PIFA with dual-resonant modes is disclosed by Chen in 2002. The resonant points of the PIFA are at 900 MHz and 1900 MHz covering frequency bands of DCS and PCS. The PIFA can thus be used in triple-band (GSM/DCS/PCS) operation (Compact PIFA for GSM-DCS-PCS triple-band mobile phone, IEEE Antennas and Propagation Society International Symposium, pages 528–531, 2002). Accordingly, by cutting a conducting plane in different manners, planar inverted-F antennas (PIFA) with different electromagnetic characteristics can be created. However, when a triple-band PIFA with accurate resonant points is produced, repeated and complex designs are required. Furthermore, when the triple-band PIFA is applied to different mobile telecommunication devices, repeated and complex adjustments are required.
Hence, there is a need for an improved triple-band PIFA built into a mobile telecommunication device. The profiles and relative positions of radiation members in the triple-band PIFA are adequately designed to accomplish triple-band operation for mobile telecommunication.